1. Field of the Invention
This invention relates to ferrite materials which are suitably used in electronic parts typical of which are electroceramics and which have good high frequency characteristics.
2. Description of the Prior Art
In recent years, there is a great tendency toward miniaturization and high performance of electronic appliances. Similar tendencies are shown toward various parts constituting the electronic appliances and also various materials therefor. For instance, with ferrites which are essential for switching power sources, magnetic heads and the like, there is a demand of the development of materials which have better high frequency characteristics in order to achieve miniaturization of the SW power sources and the high performance of the magnetic head.
Examples of ferrites having a small size and good high frequency characteristics include polycrystalline products which are obtained, for example, by subjecting aqueous solutions of starting materials to wet coprecipitation reaction to obtain fine particles of a coprecipitation ferrite material and then the fine particles to sintering. Since the coprecipitation ferrite material has a spinel phase, any calcination technique is not necessary, unlike known ceramic processes. The sintered product can be obtained by a simple process including drying, molding and sintering, coupled with another advantage that the a uniform composition is obtained, thus the coprecipitation ferrite material being suitable for use as a starting powder for ferrites.
However, where ferrites are prepared from the coprecipitation ferrite material, the spinel crystals are apt to be decomposition at the time of the sintering, thereby presenting the problem that the resultant final product has fine cracks involved therein, with mechanical durability and magnetic characteristics being degraded.
In order to obtain ferrites having good characteristics from the starting coprecipitation ferrite materials, it has been considered necessary to resort to a specific sintering procedure. For instance, there are known techniques which are disclosed in Japanese Laid-open Patent Application Nos. 60-141669 and 1-152707. The procedure set out in the Japanese Laid-open Patent Application No. 60-141669 includes heating in an atmosphere of a mixed gas of N.sub.2 and H.sub.2 gases at a given heating rate and then sintering. The procedure of Japanese Laid-open Patent Application No. 1-152707 includes sintering in vacuum or in an atmosphere of an inert gas such as N.sub.2 gas or H.sub.2 gas at a given heating rate. Moreover, Japanese Laid-open Patent Application No. 63-252929 sets forth a procedure wherein the content of divalent iron in starting materials is properly controlled to suppress pores from being formed at the time of the thermal treatment, ensuring forming of a high density product.
However, these procedures should require complicated steps such as of using a specific type of sintering atmosphere and severe control of the heating rate, thus being not satisfactory with respect to the productivity and mass-production.
On the other hand, with magnetic heads such as video heads, single crystal ferrite heads have now been changed to composite magnetic heads made of single crystal ferrites and polycrystalline ferrites in order to reduce sliding noises and to improve the CN ratio.
The composite magnetic head has a single crystal ferrite having a high saturation magnetization flux density at the side of a front gap and a polycrystalline ferrite having a high permeability at the side of a back gap. This type of head is advantageous in that although simple in structure, the head shows good electromagnetic conversion efficiencies and is enabled for high density recording.
The composite ferrite used as the magnetic core of the composite magnetic head is obtained, for example, by preparing both a single crystal ferrite and a polycrystalline ferrite and hot pressing both ferrites. Thus, the known process of fabricating a composite ferrite requires a number of steps, thus being very disadvantageous from the standpoint of reduction of the production costs.